A more thorough explanation:

The Navy Department is a part of the Department of Defense that is responsible for overseeing the operations and efficiency of the Navy, including the Marine Corps component and the U.S. Coast Guard when operating as a naval service. It was established in 1798 and is headed by the Secretary of the Navy, who is appointed by the President and reports to the Secretary of Defense.

• The Navy Department is responsible for ensuring that the Navy and Marine Corps are ready to defend the country at all times.
• The Secretary of the Navy is the head of the Navy Department and is responsible for making sure that the Navy and Marine Corps have the resources they need to carry out their missions.
• During times of war, the Navy Department works closely with other branches of the military to coordinate operations and ensure that the country is protected.

These examples illustrate how the Navy Department is responsible for overseeing the Navy and Marine Corps and ensuring that they are ready to defend the country. The Secretary of the Navy plays a key role in this process by providing leadership and resources to the Navy and Marine Corps. During times of war, the Navy Department works closely with other branches of the military to ensure that the country is protected.